This application claims priority under 35 U.S.C. §119(a) on Patent Application Nos. 2011-050658 filed in Japan on Mar. 8, 2011, and 2011-051271 filed in Japan on Mar. 9, 2011, the entire contents of which are herein incorporated by reference.
The present invention relates to an image forming apparatus in which a recording paper to which a toner image has been transferred is guided by a guide member and transported to a nip region between rotatable members and the toner image is fixed to the recording paper at the nip region.
Examples of this sort of image forming apparatuses include electrographic apparatuses. In apparatuses of this type, an electrostatic latent image is formed on an image carrier, the electrostatic latent image on the image carrier is developed using a toner, and, thus, a toner image is formed on the image carrier. Then, the toner image formed on the image carrier is transferred from the image carrier to a recording paper, the recording paper is guided by a guide member so as to pass through a nip region between two rotatable members (rollers or rotatable belts), heat and pressure are applied to the recording paper at the nip region, and, thus, the toner image is fixed to the recording paper.
FIG. 12 is a cross-sectional view schematically showing the vicinity of a guide member and rotatable members. In FIG. 12, a fixing device 101 has a heat roller 102 and a pressure roller 103 (rotatable members), the heat roller 102 and the pressure roller 103 are caused to press each other forming a nip region N between the heat roller 102 and the pressure roller 103. A guide plate 104 (guide member) is disposed on the upstream side in a recording paper P transport direction of the nip region N.
After the toner image is transferred, the recording paper P is transported to the guide plate 104, guided by a guide face 104a of the guide plate 104, and sent along a transport direction F to the fixing device 101. The heat roller 102 is disposed on the path after the guide face 104a in the transport direction F (on the downstream side in the transport direction F), and, thus, the leading edge of the recording paper P abuts against the surface of the heat roller 102. Then, the leading edge of the recording paper P (the edge on the downstream side in the recording paper P transport direction) is moved and guided to the nip region N by the surface of the heat roller 102 that is rotating in the arrow direction, the recording paper P is conveyed through the nip region N and subjected to the application of heat and pressure, and, thus, the toner image is fixed to the recording paper P.
Here, the recording paper P is transported from the guide face 104a of the guide plate 104 to the surface of the heat roller 102, and moved and guided to the nip region N by the surface of the heat roller 102 that is rotating in the arrow direction. In the transportation of the recording paper P, a paper transport path S of the recording paper P from the guide plate 104 to the nip region N is curved. Accordingly, the recording paper P slides across an end portion 104b of the guide plate 104 and is introduced into the nip region N in a tensioned state, and, thus, the recording paper P is prevented from being creased at the nip region N.
Furthermore, for example, the guide plate 104 is a metal plate and conductive, and is grounded. When the recording paper P is moved across the guide face 104a of the guide plate 104 while keeping contact therewith, static electricity may be generated on the guide plate 104, or charge on the recording paper P (charge on the toner) may be shifted to the guide plate 104, but, since the guide plate 104 is grounded, the charge on the guide plate 104 flows out from the guide plate 104 to the grounded point, and the guide plate 104 is prevented from being charged. If the charge accumulates on the guide plate 104, spark discharge occurs between the recording paper P and the guide plate 104, and the toner image on the recording paper P is disarranged.
Examples of conventional techniques include a technique described in JP 2008-83368A in which a charge removal brush is disposed at a guide face of a guide member for guiding a recording paper, so that charge is effectively removed from the recording paper by the charge removal brush.
Furthermore, examples of conventional techniques also include a technique described in JP H11-109690A in which a contact portion that is charged to the same polarity as a toner through friction with a recording paper is disposed at a guide face of a transportation guide for guiding a recording paper, so that the toner on the recording paper is prevented from being disarranged.
Generally, after a toner image is formed on an image carrier, a recording paper is conveyed through a nip region between the image carrier and a transfer roller, and the toner image is transferred from the image carrier to a front face of the recording paper, and, thus, the toner on the image carrier is not directly transferred to a back face of the recording paper. However, when toner images are repeatedly transferred at the nip region between the image carrier and the transfer roller, some toner becomes attached to the transfer roller, and the toner on the transfer roller is transferred to the back face of the recording paper. Accordingly, in the configuration in which the recording paper P slides across the end portion 104b of the guide plate 104 as shown in FIG. 12, the back face of the recording paper may be rubbed against the end portion 104b of the guide plate 104, and a slight amount of toner attached to the back face of the recording paper may become attached to and accumulate on the end portion 104b of the guide plate 104.
In particular, when the guide plate 104 is grounded as shown in FIG. 12 in order to prevent spark discharge from occurring between the recording paper P and the guide plate 104, charge on the recording paper P (charge on the toner) flows out via the guide plate 104, and the charge on the toner is reduced, and, thus, the toner on the back face of the recording paper P easily becomes attached to the end portion 104b of the guide plate 104, and the notable phenomenon occurs in which the toner becomes attached to and accumulates on the end portion 104b of the guide plate 104.
Then, when a trailing edge of the recording paper P slides across the end portion 104b of the guide plate 104, the toner attached to and accumulating on the end portion 104b of the guide plate 104 is transferred back to the trailing edge, and the trailing edge of the recording paper P is smeared.
Conventionally, such a toner attached to and accumulating on the end portion 104b of the guide plate 104 is left as it is, and this problem cannot be prevented.
For example, the charge removal brush in JP 2008-83368A or the contact portion in JP H11-109690A cannot prevent a toner from becoming attached to or accumulating on the end portion 104b of the guide plate 104.
The present invention was made in view of the above-described conventional problem, and it is an object thereof to provide an image forming apparatus in which a toner on a back face of a recording paper can be prevented from becoming attached to and accumulating on an end portion of a guide plate.